With the stress and pressure to manufacture an exorbitant number of iPhone 5s, Foxconn has hit a roadblock that could cause delays in the production of Apple’s popular phone. China Labor Watch sent out an alert on Friday notifying recipients that between 3,000 and 4,000 workers have ceased working and are protesting the reportedly grueling conditions that production workers have been subjected to.

It’s not the first time that Foxconn workers have gone on strike. In January, many workers striked after a string of employee suicides over low wages and desolate working conditions caught the eye of the public.

The production of iPhones was halted today, and it’s not yet known if Foxconn employees have returned to work. But the incident is an indication that Chinese workers do want, and are beginning to demand, improved working conditions and management practices.

The issue, according to the statement by China Labor Watch, purportedly stemmed from altercations between workers and quality control inspectors. After enacting stricter quality control standards, Foxconn workers were not sufficiently trained to learn the new skills necessary to up quality control. “This led to workers turning out products that did not meet standards and ultimately put a tremendous amount of pressure on workers,” the China Labor Watch explains.

Based on the statement, it appears that the standards were raised by both Apple and Foxconn and named “indentations standards of 0.02mm and demands related to scratches on frames and back covers” as among the improvements inspectors were requiring from line workers.

Consequently, the production workers and quality control inspectors began to butt heads, leading to several physical altercations. According to workers, there was a fight between workers and quality control inspectors in “area K” that led to the damage in “inspection room CA,” the injury of some people, and the hospitalization of others. Later, a similar incident occurred in area K, once again leading to quality control inspectors being beaten up. Yesterday, inspectors in area L received physical threats.”

Fed up with physical abuse and threats by fellow Foxconn employees, the inspectors turned to the factory’s management, but the complaints were ultimately ignored. As a result of management turning a blind eye, and coupled with Foxconn taking away its employee’s vacation privileges for this coming holiday season, all day and night shift inspectors brought the production of iPhone 5s to a standstill.

 You can read the China Labor Watch report in its entirety here.